*Bovine retinal extract is an RPE culture additive first introduced
by Pfeffer et al. [20]. It is presumed to add important trophic factors
to the RPE culture and is prepared by homogenizing 12 fresh bovine
retinas per 100 ml CMF-BSS and stirring overnight in the cold in the
dark. The mixture is cleared by centrifugation (12,000x g for 20 min).